In recent years, different types of wireless networks have been developed to provide radio communication for various wireless devices in different areas such as cells. The wireless networks, also commonly referred to as cellular or mobile networks, are constantly improved to provide better capacity, quality and coverage to meet the demands from subscribers using services and increasingly advanced terminals for communication, such as smartphones and tablets, which often require considerable amounts of bandwidth and resources for data transport in the networks. Therefore, it is often a challenge to achieve high capacity and good performance, e.g. in terms of high data throughput, low latency and low rate of dropped or lost data, in the radio communication between base stations in the wireless network and various wireless devices communicating with the base stations.
In the field of radio communication in wireless networks, the terms “wireless device” and “User Equipment, UE” are commonly used and will be interchangeably used in this disclosure to represent any mobile phone, tablet, Machine-to-Machine (M2M) device or laptop computer capable of radio communication with a wireless network including receiving downlink signals transmitted from a serving network node and sending uplink signals to the network node. Sometimes the term “user” is used instead of UE. Further, the terms “network node”, “base station” and “Node B” may be interchangeably used in this disclosure to represent any node of a wireless network that can communicate uplink and downlink radio signals with wireless devices or UEs. The network node described here may, without limitation, be a base station or any other node that controls transmissions in the network.
In order to improve capacity and performance in the wireless network, various features can be employed that are intended to make the radio communication more efficient in terms of resource usage. In particular, it is desirable to reduce the amount of interference generated by uplink transmissions made by wireless devices, which in turn could improve the capacity and performance. For example, transmissions with high bitrate may generate high interference for others. High bitrate may also require a high Signal-to-Interference Ratio, SIR, for successful communication. Since the signal strength is limited by the available device power, the SIR in a multi-user scenario may be severely degraded, leading to much lower maximum bitrate for the devices and also a lower overall system throughput.
This interference issue may be addressed by employing a so-called “clean carrier” which is dedicated to high bitrate transmissions in a Time Division Multiplexing, TDM, scheme where uplink transmissions are separated in different Transmission Time Intervals, TTIs, assigned to the wireless devices. Thereby, less rigorous power control can be employed since transmission on this carrier will not disturb transmissions on other carriers separated in frequency. In general, it is of interest for network operators to improve capacity in their networks by utilizing the available radio resources as efficiently as possible. In a TDM scheme the radio resources are commonly defined by time and frequency where only one wireless device at a time is allowed to transmit on a particular frequency, i.e. during separate TTIs, which is well-known in this field. This process is controlled by signaling so-called grants to the wireless devices.
However, it is a problem that the process of controlling uplink transmissions, e.g. in a TDM scheme, may sometimes require much signaling between the wireless devices and the network nodes for multiplexing different wireless devices in separate TTIs. Another problem is that conventional signaling may result in less than optimal utilization of available radio resources in terms of carriers and TTIs, such that some TTIs may go unused as a result of the currently employed signaling schemes, which is ultimately a waste of capacity.